The present invention relates to the technical field of a brake system that controls the rotation of a rotation member, the technical field of a seatbelt retractor for retracting a seatbelt extractably and having an energy absorption mechanism (hereinafter, referred to as an EA mechanism) for absorbing impactive energy to the occupant, with the seatbelt in a fastened state, by limiting a load applied to the seatbelt by torsional deformation of a torsion bar when high deceleration is applied to a vehicle in an emergency such as a crash, and the technical field of a seatbelt system having the seatbelt retractor.
Seatbelt systems generally mounted to vehicles such as cars prevent occupants from flying out of seats by restraining the occupants with seatbelts in an emergency, thereby protecting the occupants.
Such seatbelt systems have a seatbelt retractor for retracting a seatbelt. With such seatbelt retractors, seatbelts are retracted around a spool when not fastened but, when fastened, they are extracted and worn on the occupants. In the emergency described above, the locking mechanism of the seatbelt retractors is activated to prevent the rotation of the spool in the belt extracting direction, thereby preventing the extraction of the seatbelts. Thus, the seatbelt restrains occupants reliably to protect them in an emergency.
With the conventional seatbelt retractors, the occupants move forward by a large inertial force because of significant vehicle deceleration that is generated when the seatbelts restrain the occupants to protect them in an emergency such as a car crash. Accordingly, the seatbelts are subjected to a great load and so the occupants receive a significant impact from the seatbelts. It is therefore desirable to limit the impact applied to the occupants, although it is not so serious problem for the occupants.
Accordingly, seatbelt retractors have been developed which have a torsion bar to absorb and ease the impactive energy by limiting the load applied to a seatbelt in an emergency in a seatbelt fastened condition. (See, for example, Japanese Unexamined Patent Application Publication No. 2001-58559 (incorporated by reference herein)).
FIG. 21 is a longitudinal sectional view of an example of a seatbelt retractor disclosed in JP 2001-58559. In the drawing, reference numeral 1 denotes a seatbelt retractor; numeral 2, a U-shaped frame; numeral 3, a seatbelt; numeral 4, a spool supported rotationally between both side walls of the frame 2, for retracting the seatbelt 3; numeral 5, deceleration detection means activated by detecting high vehicle deceleration generated in the aforesaid emergency; numeral 6, a locking mechanism activated by the deceleration detection means 5 to prevent at least the rotation of the spool 4 in the belt extracting direction; numeral 7, a torsion bar fitted and passed through with play in the center of the spool 4 in the direction of the axis, for rotationally connecting the spool 4 and the locking mechanism 6; numeral 8, spring means for normally biasing the spool 4 via a bush 10 in the belt retracting direction by the spring force of a spiral spring 9; numeral 11, a pretensioner activated in the emergency to generate a belt retracting torque; and numeral 12, a bush for transmitting the seatbelt retracting torque of the pretensioner 11 to the spool 4.
The locking mechanism 6 has a locking base 14 (corresponding to a locking member of the present invention) which can rotate with a first torque transmission portion 17 of the torsion bar 7 and which retains a pawl 13 such that it can rock, the torsion bar 7 having a lock gear 6a which rotates with the torsion bar 7 under normal conditions and stops at the activation of the deceleration detection means 5 in an emergency to generate relative rotation difference between it and the torsion bar 7 to bring the pawl 13 into engagement with an internal gear 19 on the side wall of the frame 2, thereby stopping the rotation of the locking base 14 in the seatbelt extracting direction. The locking base 14 has a male screw shaft 15. Into the male screw shaft 15, a nut-like stopper 16 which rotates with the spool 4 is screwed.
The torsion bar 7 also has the first torque transmission portion 17 which is in engagement with the locking base 14 such that it cannot rotate relative thereto and has a second torque transmission portion 18 which is in engagement with the spool 4 such that it cannot rotate relative thereto.
The spool 4 is normally biased in the seatbelt retracting direction by the spring force of the spring means 8 via the bush 10, the torsion bar 7, the second torque transmission portion 18 of the torsion bar 7, and a bush 12. A belt retracting torque generated in the pretensioner 11 is transmitted to the spool 4 via the bush 12 during the operation of the pretensioner 11 and thus the spool 4 retracts the seatbelt 3 by a specified amount.
The related-art retractor 1 with such a structure completely retracts the seatbelt 3 by the basing force of the spring means 8 when the seatbelt 3 is not fastened. When the seatbelt 3 is extracted at a normal speed to wear it, the spool 4 rotates in the seatbelt extracting direction to extract the seatbelt 3 smoothly. After a tongue (not shown) which is provided slidably to the seatbelt 3 has been retained in a buckle (not shown) fixed to the vehicle body, the excessively extracted seatbelt 3 is retracted by the spool 4 by the biasing force of the spring means 8 and as such, the seatbelt 3 is fitted in such a degree that applies no feeling of pressure.
The seatbelt retracting torque generated by the pretensioner 11 is transmitted to the spool 4 in the emergency. The spool 4 retracts the seatbelt 3 by a specified amount to firmly restrain the occupant. On the other hand, the deceleration detection means 5 is activated by large deceleration generated in the emergency to activate the locking mechanism 6. In other words, the rotation of the lock gear 6a in the seatbelt extracting direction is stopped by the activation of the deceleration detection means 5, so that the pawl 13 of the locking mechanism 6 is rotated to come into engagement with the internal gear 19 on the side wall of the frame 2. This stops the rotation of the locking base 14 in the seatbelt extracting direction and so, the torsion bar 7 is twisted and only the spool 4 rotates relative to the locking base 14 in the seatbelt extracting direction. Thereafter, the spool 4 rotates in the seatbelt extracting direction while twisting the torsion bar 7. Thus, the load applied to the seatbelt 3 is limited by the torsional torque of the torsion bar 7 and so the impact applied to the occupant is absorbed and eased.
Since the spool 4 rotates relative to the locking base 14, the stopper 16 which rotates with the spool 4 rotates relative to the screwed male screw shaft 15. Thus, the stopper 16 moves toward the locking base 14. When the stopper 16 comes into contact with the locking base 14, further rotation of the stopper 16 is stopped and so the rotation of the spool 4 is also stopped, so that the torsion of the torsion bar 7 stops. Thus, the extraction of the seatbelt 3 is prevented and so the occupant is securely restrained by the seatbelt 3 and the maximum torsion of the torsion bar 7 is limited and so the torsion bar 7 is prevented from being cut off by torsion.
The related-art retractor 1 is constructed such that the locking base 14 of the locking mechanism 6 rotates relative to the lock gear 6a in the seatbelt extracting direction even in sudden extraction of the seatbelt. Accordingly, the pawl 13 of the locking mechanism 6 is brought into engagement with the internal gear 19 on the side wall of the frame 2 to prevent the rotation of the locking base 14. Therefore, the rotation of the spool 4 in the seatbelt extracting direction is prevented via the torsion bar 7 and so the extraction of the seatbelt is stopped.
Furthermore, JP 2001-58559 discloses the retractor 1 in which the limit load (FL) can be switched. Specifically, as shown in FIG. 22, a lock pin 21 of an EA-load switching mechanism 20 normally prevents a locking member 22 from ejecting from a cylinder 23. When the rotation of the locking base in the seatbelt extracting direction is stopped at a great impact when the pretensioner is activated, also the rotation of a gear 24 provided to the locking base in the same direction is stopped. Thus the rotation of a gear 25 which is normally in engagement with the gear 24 is also stopped. Since the seatbelt 3 is extracted by the inertial force of the occupant, the spool 4 continues to rotate in the seatbelt extracting direction. Therefore, a gear 26 provided rotatably with the spool 4 also rotates in the same direction and a gear 27 which is normally in engagement with the gear 26 also rotates.
On the other hand, in the initial stage after the great crash, the locking member 22 is ejected from the cylinder 23 by the spring force of a spring 28 because the lock pin 21 is pushed away by the exhaust gas from the pretensioner. Then a ratchet claw 29a of a lock wheel 29 comes into engagement with the locking member 22, thereby stopping the rotation of the lock wheel 29 in the seatbelt extracting direction. Therefore, a second torsion bar 30 is twisted at the portion of a length η shorter than the entire length θ thereof. Thus, the EA operation by the EA mechanism is started by the torsion of the first torsion bar 7 and the torsion of the portion η of the second torsion bar 30, where FL load F1 at that time is relatively high, as shown in FIG. 23. In the stage following the initial stage, the portion η of the second torsion bar 30 is twisted by a specified amount to be broken. After the second torsion bar 30 has been broken, only the first torsion bar 7 is twisted to allow EA operation, where FL load F2 at that time is lower than that in the initial stage, as shown in FIG. 23. In that way, the FL load is switched to allow the limit road applied to the seatbelt to be set flexibly in various levels depending on the occupant restraint condition with an airbag etc. in an emergency.
However, with the seatbelt retractor 1 disclosed in JP 2001-58559, as described above, the ratchet claw 29a of the lock wheel 29 is brought into engagement with the locking member 22 that has sprung out from the cylinder 23 by the spring force of the spring 28 in the initial stage after the crash, thereby preventing the rotation of the lock wheel 29 in the seatbelt extracting direction. Briefly, the cylinder 23, the locking member 22, the spring 28, and the ratchet claw 29a construct a brake system for stopping the rotation of the lock wheel 29.
However, in this brake system, a relatively large force is applied to the locking member 22 when the ratchet claw 29a comes into engagement with the locking member 22. Therefore, the locking member 22 must be increased in strength and as such, the cylinder 23 and the locking member 22 must be increased in size and also the spring 28 must be increased in spring force, thus posing the problem that the entire brake is increased in size.
Moreover, since the locking member 22 is projected to the rotating lock wheel 29 so that the locking member 22 comes into engagement with the ratchet claw 29a of the lock wheel 29, the locking member 22 is given a relatively high impactive force from the ratchet claw 29a at the engagement. This results in the necessity of increasing the cylinder 23 and the locking member 22 in size.